The invention refers to a plate heat exchanger comprising a plate package with a plurality of heat exchanger plates, each of which extends in parallel with a main extension plane, and at least one strengthening plate, wherein the heat exchanger plates are provided beside each other and form a plate package with first plate interspaces for a first medium and second plate interspaces for a second medium, wherein each of the heat exchanger plates has four portholes which form ports extending through the plate package, wherein the heat exchanger plates include an outermost heat exchanger plate at one side of the plate package and an outermost heat exchanger plate at an opposite side of the plate package, wherein two of the plate interspaces in the plate package form a respective outermost plate interspace at a respective side of the plate package, which are delimited outwardly by a respective one of the outermost heat exchanger plates, for example see U.S. Pat. No. 4,987,955 A.
In many applications for permanently joined, for instance brazed, plate heat exchangers, a high strength is required. This is important when the working pressure of one or both of the media conveyed through the plate heat exchanger is high or when the working pressure for one or both of the media various over time. Plate heat exchangers are pressure tested before delivery. It is desirable to achieve such a strength and rigidity of the plate heat exchanger that the plastic deformation in connection with the pressure testing is as small as possible.
In order to meet requirements of higher strength it is known to use thicker end or strengthening plates, i.e. the two plates located at the outermost position in the plate package. These strengthening plates may also be designated as adapter plates or frame and pressure plates. It is also known to use sheets, washers or thick plane plates as strengthening plates. Such sheets, washers or thick plane plates may also be provided outside the frame and/or pressure plates. A disadvantage of such additional plates, washers or the like is that the manufacturing becomes more complicated since more components have to be fixed when the plate heat exchanger is produced, for instance when it is brazed.
Another disadvantage of thicker strengthening plates with more material is that the thermal “slowness” increases for this strengthening plates. Due to this higher thermal slowness of the strengthening plates, a reduced thermal fatigue performance of the plate heat exchanger is obtained, in particular in the heat exchanger plates which are provided most adjacent inside the strengthening plates. Since the heat exchanger plates are manufactured of a thinner material, they will more rapidly be adapted to the temperature of the media, which results in an undesired temperature difference between the heat exchanger plates and the strengthening plates, and thus to thermally dependent stresses.
Furthermore, thicker strengthening plates result in the disadvantage that the consumption of material becomes larger and thus the costs for the plate heat exchanger increase.
U.S. Pat. No. 4,987,955 discloses a plate heat exchanger comprising a plurality of plates extending in parallel with a main extension plane. The plates comprise a plurality of heat exchanger plates and at least one strengthening plate. The heat exchanger plates are provided beside each other and form a plate package with first plate interspaces for a first medium and second plate interspaces for a second medium. Each of the heat exchanger plates has four portholes which form ports extending through the plate package. The heat exchanger plates comprises an outermost heat exchanger plate at one side of the plate package and an outermost heat exchanger plate at an opposite side of the plate package. Two of the plate interspaces in the plate package form a respective outermost plate interspace at a respective side of the plate package, which are delimited outwardly by a respective one of the outermost heat exchanger plates. The strengthening plate is provided beside and outside one of the outermost heat exchanger plates.